CN107607944A - Forward-looking imaging device based on terahertz frequency band transmission type aperture coding - Google Patents

Abstract

The invention provides a forward-looking imaging device based on terahertz frequency band transmission type aperture coding, which comprises: the terahertz wave imaging device comprises a transmission type coding aperture, a transmitting link and a receiving link, wherein the transmitting link is used for transmitting terahertz waves through the transmission type coding aperture in the radial imaging scanning area, the receiving link is used for receiving the terahertz waves generated by radiation of the imaging scanning area through the transmission type coding aperture, and when the terahertz waves pass through the transmission type coding aperture, a coding random phase shift factor and a lens phase modulation factor are loaded on the transmission type coding aperture. Through loading the lens phase modulation factor to the transmission type coded aperture, the terahertz wave beam direction is rapidly regulated and controlled, the echo is scattered by the electron bunching, and stable and rapid scanning imaging can be carried out on the target. Thereby realizing the miniaturization and low cost of the radar forward-looking imaging system.

Description

Forward-looking imaging device based on terahertz frequency band transmission aperture coding

technical field

The invention relates to the technical field of high-resolution radar staring imaging, in particular to a forward-looking imaging device based on terahertz frequency band transmission aperture coding.

Background technique

With the development of society, radar high-resolution imaging plays an increasingly important role in ensuring national strategic security and promoting national economic development. Existing radar imaging systems include microwave radar imaging systems and optical radar imaging systems. Among them, the optical sensor can perform forward-looking imaging, has short wavelength, high resolution, and fast imaging speed, but relies on target radiation, has poor penetration ability to smoke, dust, fog, and obstacles, and is easily affected by environmental factors. Microwave radar sensors can actively detect and have strong penetrating ability. However, due to the low microwave frequency and long wavelength, the angular resolution is low, and due to the limitation of the imaging principle, imaging accumulation time is required, and it is impossible to achieve high frame rate and high resolution imaging of the front view. Although Synthetic Aperture Radar (SAR) and Inverse Synthetic Aperture Radar (ISAR) imaging can obtain high resolution in the lateral direction through synthetic aperture, both rely on the relative motion between the radar and the target and cannot look forward to imaging. Radar and phased array radar require a large number of array elements, complex structures, and high construction and maintenance costs.

Microwave correlation imaging technology can realize high-resolution imaging under forward-looking and staring conditions. By constructing a time-uncorrelated and space-orthogonal array signal as the transmitting signal, the detection signal of the target area is obtained through calculation and deduction, and the target information is obtained through the correlation processing between the detection signal and the target echo signal. However, this method needs to construct a large-scale antenna array at the transmitting end, and it is difficult to achieve effective real-time beam pointing control.

Contents of the invention

The purpose of the present invention is to provide a forward-looking imaging device based on terahertz frequency band transmission aperture coding, which solves the problems of miniaturization, low cost, real-time and high-resolution of the system device that are difficult to realize in the existing radar forward-looking imaging technology. technical problem.

The present invention provides a front-view imaging device based on terahertz frequency band transmission aperture coding, including: a transmission coding aperture, a transmission link for transmitting terahertz waves to the imaging scanning area through the transmission coding aperture, and a transmission link for transmitting terahertz waves through the transmission coding aperture. The coded aperture receives the receiving link of the terahertz wave generated by the radiation in the imaging scanning area. When the terahertz wave passes through the coded aperture of the transmission type, the coded random phase shift factor and the phase modulation factor of the lens are loaded on the coded aperture of the transmission type.

Further, the transmitting link includes: a terahertz transmitting device and a terahertz transmitting module for emitting terahertz, the terahertz transmitting module is connected to the terahertz transmitting device, and the center of the terahertz transmitting device is at the same center as the transmissive coding aperture on the shaft;

The receiving link includes: a terahertz receiving device and a terahertz receiving module for receiving terahertz, the terahertz receiving module is connected to the terahertz receiving device, and the center of the terahertz receiving device is on the same axis as the center of the transmissive coded aperture.

Further, the terahertz transmitting device and the terahertz receiving device are transceiver multiplexing antennas for sending out terahertz to the transmissive coded aperture and receiving the terahertz beam reflected back by the transmissive coded aperture.

Further, the beams emitted by the transceiver multiplexing antenna completely cover the coded aperture of the transmissive coded aperture.

Further, the horizontal distance between the transmissive coding aperture and the imaging scanning area is within 20.0m.

Further, it also includes: a vector network analyzer for sending initial signals and processing received terahertz signals, and a system control host for controlling the transmission-type coded aperture and vector network analyzers, the system control host and the transmission-type The coded aperture is connected with the vector network analyzer; the vector network analyzer is respectively connected with the terahertz receiving module and the terahertz transmitting module.

Technical effect of the present invention:

The forward-looking imaging device based on terahertz frequency band transmission aperture coding provided by the present invention can quickly adjust the terahertz beam pointing and electronic spotlight scattering echo by loading the lens phase modulation factor on the transmission coding aperture, so that the target can be stably and quickly scan imaging. Therefore, the miniaturization and low cost of the radar forward-looking imaging system are realized.

The forward-looking imaging device based on terahertz frequency band transmission aperture coding provided by the present invention loads the aperture coding random phase shift factor on the transmission coding aperture, and randomly modulates the terahertz beam at the transmitting end and the receiving end respectively, which can effectively improve Target imaging resolution.

For details, please refer to the following description of various embodiments of the forward-looking imaging device based on terahertz frequency band transmission aperture coding according to the present invention, so that the above and other aspects of the present invention will be apparent.

Description of drawings

Fig. 1 is a schematic structural diagram of a terahertz radar high-resolution forward-looking imaging device provided by the present invention;

Fig. 2 is a schematic diagram of the workflow of the terahertz radar high-resolution forward-looking imaging device provided by the present invention;

illustration:

1. System control host; 2. Vector network analyzer; 3. Terahertz transmitting module; 4. Transmitting and transmitting multiplexing antenna; 5. Transmissive coded aperture; 6. Terahertz receiving module.

detailed description

The accompanying drawings constituting a part of this application are used to provide further understanding of the present invention, and the schematic embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention.

Referring to Fig. 1, the present invention provides a terahertz radar high-resolution forward-looking imaging device, including: a transmissive coded aperture 5, a transmission link for transmitting a terahertz wave to the imaging scanning area through the transmissive coded aperture 5, and a In the receiving link of receiving the terahertz wave generated by the radiation of the imaging scanning area through the transmissive coded aperture 5, when the terahertz wave passes through the transmissive coded aperture 5, the coded random phase shift factor and the lens phase modulation factor are loaded on the transmissive coded aperture 5 .

In order to realize imaging, the imaging scanning area needs to be set within the beam scanning range of the transmissive coding aperture 5 .

Preferably, the transmitting link includes: a terahertz transmitting device and a terahertz transmitting module 3 for emitting terahertz, the terahertz transmitting module 3 is connected to the terahertz transmitting device, the center of the terahertz transmitting device is connected to the transmissive coding aperture 5 The centers are on the same axis. The transmitting chain can be set facing the transmissive coded aperture 5 independently. When in use, the transmitting link and the receiving link can be replaced as required. According to the existing method. For example, the terahertz transmitting device and the terahertz receiving device are switched by an automatic control device.

Preferably, the receiving link includes: a terahertz receiving device and a terahertz receiving module 6 for receiving terahertz, the terahertz receiving module 6 is connected to the terahertz receiving device, the center of the terahertz receiving device is connected to the transmissive coding aperture 5 The centers are on the same axis.

Preferably, the terahertz transmitting device and the terahertz receiving device are transmitting and receiving multiplexing antennas 4 for transmitting terahertz to the transmissive coded aperture 5 and receiving the terahertz beam reflected back by the transmissive coded aperture 5; The initial signal and the vector network analyzer 2 for processing the received terahertz signal and the system control host 1 for controlling the transmissive coded aperture 5 and the vector network analyzer 2, the system control host 1 is connected with the transmissive coded aperture 5 and the vector network analyzer 2 respectively. The vector network analyzer 2 is connected; the vector network analyzer 2 is connected with the terahertz receiving module 6 and the terahertz transmitting module 3 respectively. According to this arrangement, the size of the device can be reduced, the link structure can be saved, and other unnecessary control devices can be reduced, thereby reducing the manufacturing cost of the device. The vector network analyzer 2 sends out the transmitting/receiving signal, and the transmissive coded aperture 5 loads coded random phase shift factors and lens phase modulation factors, all of which are uniformly controlled by the system control host 1 .

In one embodiment, the device includes a system control host 1 for controlling the transmissive coded aperture 5 and a vector network analyzer 2, a vector network analyzer 2 for sending initial signals and processing received terahertz signals, The terahertz transmitting module 3 for transmitting terahertz to the transceiving multiplexing antenna 4, the transmitting and receiving multiplexing antenna 4 for transmitting terahertz to the transmissive coded aperture 5 and receiving the beam reflected back from the transmissive coded aperture 5, and the transmitting and receiving multiplexed antenna 4 for loading the code The transmissive coding aperture 5 of the random phase shift factor and the lens phase modulation factor and the terahertz receiving module 6 used to receive the terahertz wave returned by the transceiver multiplexing antenna 4 and transmitted to the vector network analyzer 2 . The system control host 1 is connected to the vector network analyzer 2 and the transmission coded aperture 5 respectively.

The vector network analyzer 2 is signal-connected with the terahertz receiving module 6 and the terahertz transmitting module 3 . The terahertz receiving module 6 and the terahertz transmitting module 3 are signal-connected to the transmitting and receiving multiplexing antenna 4 at the same time. The transmit-receive multiplexing antenna 4 is radiatively connected to the transmissive coded aperture 5 .

The central points of the transceiver multiplexing antenna 4 and the transmissive coding aperture 5 are on the same axis z-axis, and the z-axis is parallel to the bisector of the beam emitted by the transmitting and receiving multiplexing antenna 4 and perpendicular to the transmissive coding aperture 5 . Signals are transmitted and received through the multiplexed antenna 4 . The device adopts a transmissive coded aperture 5 and a partially multiplexed transceiver link structure, which reduces the volume and cost of the radar forward-looking imaging system.

Referring to Figure 2, when the device is in use, first analyze the transmission link process, the vector network analyzer 2 is responsible for generating the initial signal, the initial signal is multiplied by the terahertz transmission module and amplified to obtain the terahertz signal, at this time the transceiver multiplexes the antenna 4 is the transmission mode, the terahertz signal is radiated to the transmissive coded aperture 5 through the transceiver multiplexing antenna 4, the transmissive coded aperture 5 is connected to the system control host 1, and the transmissive coded aperture 5 is simultaneously loaded with the aperture under the control of the system control host 1 Encode the random phase shift factor and the lens phase modulation factor, and perform aperture encoding and phase modulation on the terahertz beam radiated by the transceiver multiplexing antenna 4, and further transmit the terahertz beam to the space where the imaging scanning area is located to beam the imaging scanning area scanning. After scanning, the scattered echo signal on the surface of the imaging scanning area passes through the transmissive coding aperture 5 again. At this time, the transmissive coding aperture 5 is also loaded with the aperture coding random phase shift factor and the lens phase modulation factor under the control of the system control host 1. The lens phase modulation factor is adjusted to focus the reflected wave near the transceiver multiplexing antenna 4, and the random phase shift factor is changed to perform aperture encoding and phase modulation on the reflected beam again. Finally, the transceiver multiplexing antenna 4 switches to the receiving mode, and the transmitting and receiving multiplexing antenna 4 receives the echo signal radiated by the transmissive coded aperture 5 and transmits it to the terahertz receiving module 6, where the terahertz receiving module 6 undergoes low-noise amplification and frequency mixing After the quadrature demodulation and processing, it is returned to the vector network analyzer 2, and then transmitted to the system control host 1 for imaging processing, and finally the image of the imaging scanning area is obtained.

Wherein, the imaging processing performed by the system control host 1 refers to performing imaging processing in combination with existing object sparseness characteristics and data processing technologies such as compressed sensing, which can be performed according to this existing method.

The present invention uses the transmissive coded aperture 5 to perform a random phase shift on the incident terahertz beam and the scattered echo in the transmitting link and the receiving link respectively, which can effectively improve the time-space independence of the terahertz signal, and effectively improve the previous Depending on the imaging resolution. The lens phase modulation factor in the receiving link of the present invention focuses the scattered echo to the vicinity of the transmitting and receiving multiplexing antenna, thereby improving the signal-to-noise ratio of the device.

The device provided by the present invention is based on the basic principle of terahertz aperture coding imaging. Through the terahertz transmitting module, the transmissive coding antenna, the terahertz receiving module and the system control host, the quasi-optical technology is used to regulate the terahertz beam pointing and spot size. Realize the simplicity and miniaturization of the system device, and improve the imaging resolution and imaging speed. Transmissive aperture coding in the terahertz frequency band can only be used for spatial modulation of electromagnetic waves.

The invention realizes forward-looking high-resolution imaging for short-distance targets, and can be applied to short-distance imaging fields such as security inspection and anti-terrorism, target detection and identification, chemical identification, medical imaging, and quality control. The imaging device has the advantages of high resolution, high frame rate, real-time and miniaturization.

Preferably, N array elements are evenly arranged in the vertical direction of the transmissive coded aperture 5, and the pitch of a single array element is 1:N, and the array element spacing is determined according to the transmitted terahertz wavelength, generally 1-5 terahertz wavelength. The height of the transmissive coded aperture 5 in the vertical direction is h,

At this pitch, aperture coding and phase modulation can be performed on the terahertz wave radiated by the transceiver multiplexing antenna 4 on a smaller unit scale, so as to obtain the optimal coding effect and beamforming capability. Its specific value is determined by the processing technology of the transmissive coded antenna. Taking the transmissive array antenna based on metamaterials as an example, the pitch of the array element can reach hundreds of microns.

Preferably, the beam emitted by the transceiver multiplexing antenna 4 completely covers the coded aperture of the transmissive coded aperture 5 . Determined by the size of the transmissive coded aperture 5 and the beamwidth of the transceiver multiplexing antenna 4 , the imaging effect is the best when the transmit beam can completely cover the coded aperture.

Preferably, the horizontal distance between the transmissive coded aperture 5 and the imaging scanning area is within 20.0m. Setting this distance can achieve the best detection effect of short-distance imaging.

In the device provided by the present invention, the system control host 1 generates a corresponding phase distribution diagram according to the random phase shift factor of the aperture encoding in formula (1), and inputs it to the transmissive encoding aperture 5 to complete the phase loading;

P _C =random(p _l ,p _h ,m), (1)

Wherein, p _l and p _h represent the upper limit and the lower limit of the random phase shift interval respectively, and random means that the mth array element on the vertical direction of the transmissive coded aperture 5 is applied with a uniformly distributed random phase located in the phase shift interval, m= 1,2...N.

The system control host 1 generates a corresponding phase distribution map according to the lens phase modulation factor in formula (2), and inputs it to the transmissive coded aperture 5 for phase loading;

Among them, f is the focal length of the lens, k=2πf _c /c, f _c is the center frequency of the terahertz wave, c is the speed of light, and y _m is the ordinate of the center point of the mth array element in the vertical direction of the transmissive coded aperture , m=1, 2...N, y ₀ is the ordinate at the phase center position of the lens phase modulation factor on the transmissive coded aperture 5 .

The transmissive coded aperture 5 loaded with the lens phase modulation factor acts as a digital lens, and the terahertz beam incident on the transmissive coded aperture 5 is transmitted and focused on the focal plane.

The horizontal distance d between the focal plane and the imaging scanning area is determined by formula (3):

Wherein, a is the horizontal distance between the transmitting and receiving multiplexing antenna 4 and the transmissive coding aperture 5, f is the focal length of the lens, b is the horizontal distance between the transmissive coding hole 5 and the imaging scanning area, and the focal plane refers to the space where the imaging scanning area is located The center and the transceiver multiplexing antenna 4 are about the conjugate plane of the digital lens.

The direction of the transmitted terahertz beam is consistent with the light direction of the incident beam at the phase center position y ₀ of the lens phase modulation factor on the transmissive coded aperture 5 . When the phase center position of the lens phase modulation factor (the phase center position is the value of _y0 in formula (2)) moves from the lower end of the transmission coded aperture to the upper end point, the transmitted terahertz beam can sequentially scan the imaging area. Scan block by block. The spot size formed by the transmitted terahertz beam on the surface of the imaging scanning area is s, and the maximum detectable target height of the imaging device provided by the present invention is l, and s and l should satisfy formulas (4) and (5):

On the one hand, the aperture-coded random phase-shift factor in the transmission chain can randomly shift the phase of the incident terahertz beam at each element of the transmissive coded aperture, thereby changing the spatial amplitude and phase distribution of the terahertz wave in the target area, so that Its radiation mode changes from a spherical wavefront to a random wavefront, and the aperture-encoded random phase-shift factor in the receiving link performs random phase-shifting on the terahertz echo scattered by the target again, making the echo signal more space-time independent. Combined with the sparse characteristics of the target and data processing technologies such as compressed sensing, the resolution of the imaging device can eventually exceed the diffraction limit of traditional radars of the same caliber to obtain high-resolution capabilities in the beam, and the mode switching speed is fast without imaging accumulation time.

On the other hand, the lens phase modulation factor can make the transmissive coded aperture act as a digital lens to transmit and focus the terahertz beam radiated by the transceiver multiplexing antenna in the transmission chain to the focal plane, where the focal plane refers to the target In space, it is a plane conjugate to the transceiver antenna 4 with respect to the digital lens. By changing the phase center position of the lens phase modulation factor, the direction of the terahertz beam can be controlled, so that the focal point of the beam can be translated on the focal plane, and the specific target can be detected with the same spot size, so as to realize beam scanning and avoid the imaging device from focusing on the target. The mechanical scanning of the device improves the imaging frame rate and stability of the device. In addition, in the receiving link, the scattered echo is reflected to the transmissive coded aperture 5, and the lens phase modulation factor is adjusted again. The system control host 1 generates the lens according to (2) Phase modulation factor, in order to focus scattered echoes near the transceiver multiplexing antenna, the only difference between the phase modulation factor of the lens in the receiving chain and the transmitting chain is the focal length of the digital lens, the focal length of the digital lens in the receiving chain f' is:

The focal length depends on the distance between the transceiver multiplexing antenna 4 and the transmissive coded aperture 5 , and between the transmissive coded aperture 5 and the imaging scanning area. Therefore, a better imaging effect can be achieved by simply adjusting a and b, avoiding the trouble of repeated scanning.

Taking the transmissive coded aperture based on metamaterials as an example, determine the vertical height l=0.50 m of the transmissive coded aperture, which contains 1000 array elements in the vertical direction, and the horizontal distance between the transmissive coded aperture and the antenna a= 0.50m, the horizontal distance between the coding aperture and the target is b=1.5m.

The system control host generates a corresponding phase distribution map according to the aperture coded random phase shift factor P _C =random(-0.5π,0.5π,m), and inputs it to the transmissive coded aperture to complete phase loading, where m=1,2...1000.

At the same time, the system control host according to the lens phase modulation factor Generate the corresponding phase distribution map and input it to the transmission coded aperture to complete the phase loading. Among them, the focal length of the lens in the transmitting link is f=5/12m, k=2πf _c /c, the focal length of the lens in the receiving link is f′=3/8m, the central frequency of the terahertz wave fc=300.00GHz, the speed of light _c =3×10 ⁸ m/s. y _m is the vertical coordinate of the center point of the mth array element in the vertical direction of the transmissive coding aperture, m=1,2...1000. y ₀ is the ordinate at the phase center position of the lens phase modulation factor in the vertical direction of the transmissive coded aperture. The transmissive coded aperture loaded with the lens phase modulation factor acts as a digital lens, and the incident terahertz beam is transmitted and focused on the focal plane. The horizontal distance d=1.00m between the focal plane and the target is calculated by formula (3).

When the phase center position of the lens phase modulation factor moves from the lower endpoint to the upper endpoint of the transmissive coded aperture, the transmitted terahertz beam can scan the target block by block sequentially. Calculated from formulas (4) and (5), the spot size s=0.20m formed by the transmitted terahertz beam on the target surface and the maximum detectable target height l=2m of the device are obtained.

For an imaging target with a height of 2.00m and a width of 1m, such as human security imaging, the scanning area is Δ=2.00m ² , and a total of Δ/s^2=50 scans are required to achieve complete coverage of the target by the "spot". A single switch of the metamaterial-based transmissive coded aperture takes about t=1.00ms. Therefore, it takes at least T=Δ/s^2×t=50.00ms for the imaging device to perform a complete scan of the human security inspection image in this embodiment, so the system frame rate can reach up to 20.00Hz.

Existing security inspection scanning imaging mainly adopts mechanical scanning method, and mechanical scanning can scan once in 1-2 seconds. The scanning time is too long and the imaging efficiency is low. Although the scanning speed can be provided by using the existing large array, the existing large array scanning imaging device is expensive. Increased usage costs.

It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed above, but that several changes and modifications are possible without departing from the scope of the invention as defined in the appended claims. While the invention has been illustrated and described in detail in the drawings and description, such illustration and description are illustrative or exemplary only and not restrictive.

Claims (5)

1. A front-view imaging device based on terahertz frequency band transmission aperture coding, characterized in that it includes: a transmission coding aperture, a transmission link for transmitting terahertz waves in the radial imaging scanning area through the transmission coding aperture and a receiving link for receiving the terahertz wave generated by the radiation in the imaging scanning area through the transmissive coded aperture, when the terahertz wave passes through the transmissive coded aperture, a code is loaded on the transmissive coded aperture Random phase shift factor and lens phase modulation factor. 2. The front-view imaging device based on terahertz frequency band transmission aperture coding according to claim 1, wherein the transmission link includes: a terahertz transmission device and a terahertz transmission module for emitting terahertz, The terahertz transmitting module is connected to a terahertz transmitting device, and the center of the terahertz transmitting device is on the same axis as the center of the transmissive coded aperture; The receiving link includes: a terahertz receiving device and a terahertz receiving module for receiving terahertz, the terahertz receiving module is connected to the terahertz receiving device, and the center of the terahertz receiving device is connected to the transmission code The centers of the apertures are on the same axis. 3. The front-view imaging device based on terahertz frequency band transmission aperture coding according to claim 2, characterized in that, the terahertz transmitting device and the terahertz receiving device are for transmitting to the transmission coding aperture A transceiver multiplexing antenna that emits terahertz and receives the terahertz beam reflected back by the transmissive coded aperture. 4 . The front-view imaging device based on terahertz frequency band transmission aperture coding according to claim 3 , wherein the beam emitted by the transceiver multiplexing antenna completely covers the code aperture of the transmission code aperture. 5. The front-view imaging device based on terahertz frequency band transmission aperture coding according to claim 3, wherein the horizontal distance between the transmission coding aperture and the imaging scanning area is within 20.0m.